Phillip E. Savage

Upgrading of crude algal bio-oil in supercritical water

We determined the influence of a Pt/C catalyst, high-pressure H2, and pH on the upgrading of a crude algal bio-oil in supercritical water (SCW). The SCW treatment led to a product oil with a higher heating value (∼42 MJ/kg) and lower acid number than the crude bio-oil. The product oil was also lower in O and N and essentially free of sulfur. Including the Pt/C catalyst in the reactor led to a freely flowing liquid product oil with a high abundance of hydrocarbons. Overall, many of the properties of the upgraded oil obtained from catalytic treatment in SCW are similar to those of hydrocarbon fuels derived from fossil fuel resources. Thus, this work shows that the crude bio-oil from hydrothermal liquefaction of a microalga can be effectively upgraded in supercritical water in the presence of a Pt/C catalyst.

Catalytic hydrothermal deoxygenation of palmitic acid

We herein report a new approach to convert fatty acids to hydrocarbons in near- or supercritical water. We tested several different metal salts, bases, and high-surface-area supported metal catalysts for activity toward deoxygenation of palmitic acid in a hydrothermal reaction medium. Two heterogeneous catalysts, 5% platinum on activated carbon (Pt/C) and 5% palladium on activated carbon (Pd/C), proved to be very effective for hydrothermal deoxygenation of palmitic acid. The reactions were done in water with no added H2. The catalysts can be reused without significant activity loss, and the selectivity was more than 90% toward pentadecane, the deoxygenation product. We examined the effect of the catalyst loading, reactant loading, batch holding time, and reaction temperature on the Pt/C-catalyzed deoxygenation rate. The results show that the reaction is first-order in palmitic acid, and the rate constants displayed Arrhenius behavior with an activation energy of 79 kJ mol−1.

Hydrothermal Decarboxylation and Hydrogenation of Fatty Acids over Pt/C

We report herein on the conversion of saturated and unsaturated fatty acids to alkanes over Pt/C in high-temperature water. The reactions were done with no added H(2) . The saturated fatty acids (stearic, palmitic, and lauric acid) gave the corresponding decarboxylation products (n-alkanes) with greater than 90 % selectivity, and the formation rates were independent of the fatty acid carbon number. The unsaturated fatty acids (oleic and linoleic acid) exhibited low selectivities to the decarboxylation product. Rather, the main pathway was hydrogenation to from stearic acid, the corresponding saturated fatty acid. This compound then underwent decarboxylation to form heptadecane. On the basis of these results, it appears that this reaction system promotes in situ H(2) formation. This hydrothermal decarboxylation route represents a new path for using renewable resources to make molecules with value as liquid transportation fuels.

Catalytic treatment of crude algal bio-oil in supercritical water: optimization studies

We have investigated the catalytic treatment of a crude algal liquefaction bio-oil in supercritical water to discover how the properties of the treated oil depend on the experimental conditions. An L9 (34) orthogonal array design (OAD) with four factors at three levels was employed. The four factors were temperature (varied from 430–530 °C), time (varied from 2–6 h), catalyst type (Pt/C, Mo2C, HZSM-5), and catalyst loading (varied from 5–20 wt%). We used a direct analysis to determine the relationship between experimental conditions and properties of treated oils. The oil properties we examined were elemental composition, atomic ratios, chemical composition, and higher heating value. Of the four factors, the 100 °C variation in temperature was always the most influential for each of the oil properties examined. Of the remaining three factors, catalyst type had the greatest influence on the fatty acid content of the treated oil and the fraction of N- and O-containing compounds in the oil. Catalyst loading had the greatest effect on the higher heating value and O/C ratio in the treated oil. Reaction time had the greatest effect on the H/C and N/C ratios. The results demonstrated that treatment in supercritical water at 430 °C led to roughly a halving of the N and O content of the oil, a reduction in S to below detection limits, and about a 10% improvement in the higher heating value of the bio-oil. Within the parameter space investigated, the conditions leading to the highest content of saturated compounds in the treated oil are 430 °C, 6 h, with a 10 wt% loading of Mo2C as the catalyst. Around 76 wt% of the carbon in the feedstock was retained in the treated oil at these conditions.

Phenol oxidation in supercritical water

Abstract The oxidation of phenol has been accomplished in subcritical and supercritical water. Seventy experiments were performed in an isothermal, plug-flow reactor at temperature from 300 to 420°C, pressures from 188 to 278 atm, and residence times from 4 to 111 seconds. The initial phenol concentrations ranged from 2.8 × 10−4 to 5.3 × 10−3 M, and the oxygen concentrations were between 6.5 × 10−5 and 6.4 × 10−2 M at reaction conditions. The oxidation experiments covered essentially the entire range of phenol conversions. The experimental results were consistent with the global reaction order for phenol being in the range of1/2and 1, and with the global reaction order for oxygen being greater than zero. The conversion increased with increasing pressure, which may either suggest that the reaction order with respect to water was greater than zero, or that the apparent activation volume was less than zero. A variety of reaction products were detected, including mono- and di-car☐ylic acids, dihydroxybenzenes, phenoxyphenols, and dibenzofuran, indicating that the oxidation of phenol in supercritical water may involve a complex set of multiple reactions. The concentrations of metals in the reactor effluent were very low, indicating that corrosion effects were likely not a complicating factor in this study. No metals were detected in the solid material collected in the reaction product filter, also indicating an absence of corrosion effects.

Mechanisms and kinetics models for hydrocarbon pyrolysis

Abstract Kinetics models based on the governing mechanism for a multi-step chemical reaction provide insight into the underlying chemistry and they can be extrapolated more confidently than can empirical kinetics models. The field of thermal hydrocarbon chemistry is sufficiently mature that the types of free-radical reactions that are important have been reasonably well elucidated. Moreover, rate constants for many elementary reactions have been measured experimentally, and rate constants for other reactions can be estimated from thermochemical kinetics considerations. These circumstances facilitate the development of quantitative mechanism-based mathematical models for hydrocarbon pyrolysis. This paper provides an overview of the current approaches for mechanistic modeling of hydrocarbon pyrolysis. The steps involved in developing both analytical and numerical models are described and illustrated with examples from the literature.

A general kinetic model for the hydrothermal liquefaction of microalgae.

We developed a general kinetic model for hydrothermal liquefaction (HTL) of microalgae. The model, which allows the protein, lipid, and carbohydrate fractions of the cell to react at different rates, successfully correlated experimental data for the hydrothermal liquefaction of Chlorella protothecoides, Scenedesmus sp., and Nannochloropsis sp. The model can faithfully account for the influence of time and temperature on the gravimetric yields of gas, solid, biocrude, and aqueous-phase products from isothermal HTL of a 15 wt% slurry. Examination of the rate constants shows that lipids and proteins are the major contributors to the biocrude, while other algal cell constituents contribute very little to the biocrude.

Algae Under Pressure and in Hot Water

Strategies are being developed to convert algae into high-value products and fuels without expensive drying of raw biomass. Algae grow quickly, can be cultivated to have a high oil (triacylglyceride) content, and can be grown on nonarable land with brackish or salt water. These characteristics make them an attractive source of biomass for renewable biofuels. The U.S. Navy and commercial airlines have demonstrated the use of algal biofuel in ships and planes; blending algal biofuel with ultralow-sulfur diesel fuel reduced the pollutants and particulate matter and improved fuel economy during the operation of a marine vessel on the Great Lakes (1). Algae-derived fuel is very expensive, however, and most of the cost is associated with producing the biomass. The U.S. Navy has contracted to pay

Heterogeneous catalysis in supercritical water

12 million for 450,000 gallons (1.7 million liters) of biofuel, which works out to about

Kinetics of acetic Acid oxidation in supercritical water.

27/gallon or 10 times the U.S. cost of petroleum-derived fuel [see, for example, (2)]. Chemical reactions in hot, compressed water (hydrothermal reactions) and in supercritical fluids can provide new, potentially cheaper paths to renewable fuels from wet algal biomass (3).